The present invention relates to a bayonet fastening device for the attachment of an accessory to a dispensing device, in particular for the attachment of a mixer to a two-component cartridge.
There exists a great number of mixers and cartridges having means for attaching the mixer to the cartridge for example, U.S. Pat. Nos. 4,767,026 and 4,538,920 disclose on mixer that has two bayonet locking lugs inserted into corresponding prongs on the cartridge by rotation. On one hand, the rotary locking movement of the complete mixer will cause contamination of one chemical component against the other chemical component at the interface between the cartridge and the mixer, in that these components will be transported from one outlet to the other outlet, from one inlet to the other inlet, causing an undesired reaction between these chemical components at the interface between cartridge and mixer or closure means, and eventually carrying such a reaction back into the cartridge outlets, thus causing plugging of the outlets. On the other hand there exist situations where it is necessary to connect and attach the mixer or accessory to a multiple component cartridge or dispensing device in a predetermined position, such as when cartridge outlets or mixer inlets are of a different size for different relative mixing ratios or when mixers or accessories are refitted for reuse.
There exists a need to connect and attach a mixer or accessory to a multiple component cartridge or dispensing device in a predetermined orientation, such as when cartridge outlets or mixer inlets are of a different size for different relative mixing ratios or when special high ratio mixers are used for greater mixing efficiency and when mixers or accessories are refitted for reuse. In the latter case of reuse, it is necessary to avoid any possibility of cross contamination of one chemical component against another during refitting. Such cross contamination of reactive chemical systems can cause plugging at the cartridge outlets and cause a reaction back into and within the cartridge.
U.S. Pat. No. 5,228,599 discloses a multiple dispensing cartridge having a mixer attached thereto with the aid of a coupling nut having an internal thread, wherein each storage cylinder ends in a dispensing opening which forms a side by side outlet, whereas the inlet of the mixer is not defined. The mixer is put on the cartridge and secured by a coupling nut via an external thread at the cartridge.
Another cross contamination situation can occur when a clean mixer or accessory inlet area or closure plugs are able to make any form of incorrect alignment contact, such as by angular tipping, with the chemical components at the cartridge outlet area during the process of initial placing of the mixer or closure plugs against the cartridge in preparation for attachment. In that case, when fitting the same mixer or closure plugs in the correct position, it is possible to now chemically contaminate the outlets of the cartridge. Again, this can cause plugging and a reaction back into and within the cartridge.
Additionally, it is commonly found in bayonet attachment means of the prior art that the bayonet prongs of the cartridge are relatively small and therefore of limited structural rigidity and strength. This allows the possibility of distortion and is of greater significance due to the trend towards smaller mixer diameters and therefore high backpressures, the result being leakage at the mixer to cartridge sealing interface during dispensing.